The present invention relates to a process for the reactive treatment of workpieces in which a plasma beam is produced in an evacuated recipient and, with respect to the area of the highest plasma density along the beam axis, workpieces are arranged in a radially offset manner, fresh reactive gas being charged into the recipient and used-up gas being sucked out of the recipient.
The present invention also relates to a vacuum treatment system comprising a plasma beam production arrangement, a gas inlet operatively connected with a reactive gas supply, an axially extending workpiece carrier arrangement radially set off from an axis of a plasma beam produced by the plasma beam production arrangement. The workpiece carrier arrangement mounts a rotational surface coaxial with respect to the axis of the plasma beam and a gas suction system. Moreover, the present invention is further directed to uses of the foregoing process and system such as metastable layers, including cBN-layers, .alpha.-Al.sub.2 O.sub.3 layers, C.sub.3 N.sub.4 layers, and diamond layers, which are deposited on the workpieces, and reactive chemical compounds, including free radicals, which are produced for surface treatment of the workpieces or a coating system.
Swiss Patent CH-PS 664 768 describes a coating process in which a low-voltage arc discharge with a hot cathode is used as the plasma beam. Workpieces are arranged essentially parallel to the beam axis, in a radially offset manner thereto, thus outside the area of the highest plasma density along the beam axis where reactive gas is nozzled in diametrically opposite the workpieces. The admitted reactive gas reacts in the plasma and on the surface of the workpieces to be coated. A reaction product is thus deposited as a layer on the workpiece surfaces. In addition to the remaining fresh reactive gas and the working gas, normally a precious gas such as argon, gaseous reaction products are also sucked out of the chambers. The known arrangement has a disadvantage that no pure metastable layers can be deposited in a large-surface manner.
Specifically with respect to diamond layer depositing, German Patent DE 40 29 270, which corresponds to U.S. patent application Ser. No. 757,694, utilizes a higher plasma density supposedly required for diamond depositing than Swiss Patent CH 664 768 and, at the same time, permits the homogeneous coating of larger workpiece surfaces or more workpieces simultaneously. According to German Patent 40 29 70, homogeneity with this high plasma density can only be achieved by generating a plurality of individual plasma beams side-by-side, to obtain a spatially distributed, uniformly high plasma density.
By way of an example, DE 40 29 270 describes an arrangement of the workpieces with respect to a directed plasma beam in the area of approximately 50% of the maximal plasma density. It was found, however, that with this arrangement it is difficult to achieve the same layer quality over larger surfaces in a reproducible fashion.
It is an object of the present invention to provide a treatment process in which now larger workpiece surfaces and more workpieces simultaneously can be homogeneously treated, particularly coated, in a reproducible manner. That is, they can be treated in a manner which is economical on an industrial scale, and which, as a coating process, is suitable in general for the deposition of metastable layers which are difficult to produce, particularly of diamond, cBN, .alpha.-Al.sub.2 O.sub.3 or C.sub.3 N.sub.4 layers.
This object has been achieved in accordance with the process of the present invention by providing that the workpiece surfaces to be treated in the same manner are arranged around the plasma beam along a longitudinally extending rotational surface.
As used herein, "metastable" is defined as in "Lehrbuch der anorganischen Chemie" (translation, "Inorganic Chemistry Textbook"), Holleman-Wiberg, Walter deGruyter, p. 83 (Berlin, N.Y. 1976, 81st-90th Ed.).
In contrast to the process described in German Patent DE 4 029 270, where the workpieces are arranged in the area of high plasma density of a homogeneously distributed plasma (or at least in an area of 50% of the maximal plasma density), the present invention recognizes that, when an extremely dense plasma is produced in a thin channel, particularly by a heavy-current arc, sufficiently high plasma densities can be achieved at a relatively far distance from the arc in order to be able to deposit even diamond layers there. Particularly in the heavy-current arc, such extremely high plasma densities are produced that the plasma density at the site of the substrates for the diamond deposition will amount to only a few percent of the maximal plasma density in the heavy-current arc center.